Why tetras need a tank of their own to breed
Most small tetras - neons, cardinals, glowlights, black skirts and their relatives - breed by scattering. The female releases eggs among fine plants while the male fertilises them in quick bursts, and neither parent does any caring afterwards. In a community tank those eggs are simply food: tankmates find them within hours, and the tetras themselves pick back through the plants eating their own spawn. A dedicated breeding tank solves that single problem. It gives a conditioned pair somewhere to scatter eggs where the eggs drop out of reach, and it lets you lift the parents out the moment spawning is finished rather than discovering an empty tank the next morning.
The tank and its layout
A 10 to 20 gallon tank is plenty for a pair or a small group. Keep the bottom bare glass and cover it with a layer of marbles or a mesh grille raised slightly off the glass, so eggs fall between or through and settle where adult mouths cannot follow. Run a small sponge filter at a gentle bubble - anything stronger drags eggs and newborn fry into the intake. Warm the water to roughly 76 to 79 degrees, and keep the tank dim: tape card over the sides or site it away from bright room light, because tetra eggs and newly hatched fry are light-sensitive. Fill it mostly with water from the main tank so the chemistry the adults know does not change on moving day, and fit a lid, since excited fish jump.
Water and planting for a successful scatter
Tetras spawn most willingly in soft, slightly acidic water, around pH 6.0 to 6.8 with low hardness, which also helps the eggs develop. The planting is functional rather than decorative: dense clumps of fine-leaved plants such as java moss, or artificial spawning mops hung from the surface, give the female somewhere to push into and scatter. Eggs from many tetra species are slightly adhesive and lodge among fine strands before dropping, so the thicker the thicket at one end of the tank, the more eggs survive the first hour. One large mop or moss mass is better than plants spread thinly everywhere.
Conditioning the parents and timing the spawn
Breeding fails most often because the adults were not ready. Feed the chosen fish generously on frozen and live foods - baby brine shrimp, daphnia, small worms - for a week or two until the female is visibly round with eggs and the male shows his strongest colour. Move the pair, or one female with two males, into the breeding tank in the evening. Spawning usually begins at first light, with chasing through the plants and eggs raining down in bursts over an hour or two. As soon as the chasing stops and the female looks slim again, net every adult straight back to the main tank. An hour of delay costs eggs.
Eggs, hatching and first foods
Tetra eggs hatch quickly, in about a day to a day and a half, and the fry spend their first days hanging on the glass and plants while they absorb their yolk sacs. Do not feed until they are free-swimming horizontally. Their first food has to be microscopic: infusoria, green water or a liquid fry food, offered in tiny amounts several times a day. Once they are big enough to manage it, newly hatched baby brine shrimp becomes the growth food. Change small amounts of water carefully with aged water matched to the tank, keep the light low for the first week, and expect uneven growth - the biggest fry will eat the smallest if you do not grade them by size as they grow.
Keep the whole attempt written down while it is fresh, because tetra spawns succeed or fail on details you will not remember next month: record the water values you mixed, the pairing you used and the hatch that followed in KinsLe's Pet Passport, and those notes stay with the fish as one packet for the next spawn.